Saws have been in use for centuries to cut work pieces, such as wood boards and metal bars. A wide variety of different types of saws exist, having a wide array of shapes and sizes. The shape or size of a saw type is dictated largely by the particular use to which the saw is placed.
Originally, saws were hand operated. As such, the only way in which the blade moved was through movement of the blade by the user. Recently, various types of powered saws have come into use. Most powered saws existing currently are driven either by an electric or pneumatic motor. Of the many types of saws that exist, the saw of interest to the present invention is a coping saw. A coping saw is a saw used at various angles to create a coped appearance. Coping saws are particularly useful in cutting crown moldings used in building interiors. A typical coping saw has a relatively thin, generally linear saw blade that is held at its opposite ends by a U-shaped frame. It differs from most saws, in that a coping saw blade must be supported at both of its ends. By contrast, a keyhole saw blade (as with most other saw blades) is supported either only at one end, or only at its center (with a circular saw).
Heretofore, most coping saws have been hand operated. Because of the configuration of a coping saw, it has been difficult to create an effective power driven coping saw.
One example of a powered coping saw known to applicant is shown in Adomatis U.S. Pat. No. 5,027,518. Adomatis discloses a coping saw that powers the blade by driving one side of the blade. The "driven end" saw of Adomatis' blade appears to be driven by a rotating disk that includes an eccentrically mounted pin which serves as a cam, to convert the rotary movement of the disk to reciprocal movement of the blade. The "non-driven" end of the Adomatis device is moved by a spring arrangement, and is not believed to be actively driven.
In addition to the Adomatis reference discussed above, other patents are known to applicant which relate to various types of powered saws. For example, Northall U.S. Pat. No. 1,491,134 relates to a powered saw which employs a bearing casing in which is contained a crank shaft. The crank shaft is provided with two cranks. The inner end of the crank shaft has a bearing in the side of the casing. The crank shaft is connected by means of a pitmen with the ends of the saw blade, whereby, when the crank shaft is driven, the blades will be driven in opposite directions by the cranks and pitmen.
Pearl U.S. Pat. No. 4,048,891 discloses a cutter mechanism for cutting sheet material. Pearl uses an eccentric cam mounted on a fly wheel to cause reciprocal movement of the blade. The opposite end of the blade is connected to a body which is reciprocally, slidably moveable in a slide body.
Myers U.S. Pat. No. 5,134,777 discloses the use of scotch-yoke mechanism to drive a reciprocal saw through a rotating eccentric cam. The Myers device also includes a somewhat complicated planetary gear mechanism and actuator for shifting a ring gear about its central axis to vary the stroke of the blade holder.
Lindley British Patent Specification No. 1,369,950 relates to a pneumatically driven saw which uses a scotch-yoke drive system. Lindley's scotch-yoke drive mechanism is best shown in FIG. 5 of the Lindley patent. In Lindley, the rotation of a crank lever rotates a crank pin. The crank pin engages a slot to reciprocally move the hack saw frame and hence the hack saw blade.
Although the saws discussed above likely perform their functions in a workmanlike manner, room for improvement exists. In particular, room for improvement exists in providing a powered coping saw capable of driving both ends of the saw blade so that the saw blade is "pulled" through the work piece in both directions of movement.
It is therefore one object of the invention to provide a powered coping saw which reciprocally, actively moves the blade in both directions of movement.